Update to enable the Large Address Aware (LAA) for the 32-bit version of Outlook 2016 and Outlook 2013

Applies to: Outlook 2016Outlook 2013


Assume that you use Microsoft Outlook 2016 or Microsoft Outlook 2013 for some time. Even if you have moderate memory use, the contiguous free memory space is exhausted. This causes a fragmented and non-rendering UI.

This update enables the Large Address Aware (LAA) state for the 32-bit version of Outlook 2016 and Outlook 2013 on a 64-bit operating system.

More information

To enable the LAA state and allow the 32-bit version of Outlook 2016 or Outlook 2013 to use the 4 GB extended address space, follow the steps for the appropriate Office version.

Outlook 2016

Install the May 1, 2018, update for Outlook 2016 (KB4018372).

Note No additional registry settings are required for Outlook 2016 to use LAA.

Outlook 2013

Install the May 1, 2018, update for Outlook 2013 (KB4018376).

After you install the update, set the following registry subkey value:


DWORD value: 0 (zero)

Diagnostic testing

Setting the ReserveHighAddressRange DWORD value to 1 reserves the high memory addresses that are available in the application at startup to prevent add-ins and the Outlook.exe process from allocating memory in the high address range. The only reason to do this is for diagnostic testing. For example, you can do this to determine how a COM add-in behaves when the high memory address is made available to it and also when it is removed for diagnostic work.

To use this setting, set the following registry subkey value:

HKEY_CURRENT_USER \Software\Microsoft\Office\xx.0\Outlook\ReserveHighAddressRange

DWORD value: 1

Alternatively, a developer can set the value in the following registry subkey value to 1 to reserve the low address range:

HKEY_CURRENT_USER \Software\Microsoft\Office\xx.0\Outlook\ReserveLowAddressRange

DWORD value: 1

If a developer wants to review how an add-in operates when allocations are in the high address range, they can use ReserveLowAddressRange to force subsequent allocations to be made in the high memory range. This may help identify COM add-ins that are hardcoded to use specific address ranges.

For more information, see the following Office article:

Large Address Aware in Outlook 2016